1. Field of the Invention
The present invention relates to the field of liquid crystal displaying techniques, and in particular to a liquid crystal display device that improves gamma (γ) characteristics.
2. The Related Arts
Recently, liquid crystal displaying techniques undergo fast development and become a hot spot of research. Due to the advantages of high resolution, reduced thickness, light weight, and low power consumption, the liquid crystal display devices find wide applications in the field of displaying for medical sectors, advertisements, military purposes, exhibitions, and entertainments. FIG. 1 is a schematic view illustrating the structure of a known liquid crystal display device. The known liquid crystal display device 1 comprises a liquid crystal display panel 10 and a backlight module 12. The liquid crystal display panel 10 comprises a first substrate 11, a second substrate 13, and a liquid crystal layer 15. The first substrate 11 is an electrode substrate, while the second substrate 13 is a color filter substrate. The liquid crystal layer 15 is sandwiched between the first substrate 11 and the second substrate 13. FIG. 2 is an equivalent circuit diagram of each pixel unit included in the liquid crystal display device 1. The liquid crystal display device 1 comprises a plurality of pixel unit 110 that is arranged in a matrix form. As shown in FIG. 2, each of the pixel units 110 further comprises: a scan line 1101, a data line 1102, a thin film transistor 1103, and a pixel electrode 1104.
Specifically, the scan line 1101 and the data line 1102 are arranged to cross and isolate from each other. The gate terminal of the thin film transistor 1103 is connected to the scan line 1101. The source terminal of the thin film transistor 1103 is connected to the data line 1102. The drain terminal of the thin film transistor 1103 is connected to the pixel electrode 1104. When the scan line 1101 supplies a scan signal to turn on the gate terminal of the thin film transistor 1103, the pixel electrode 1104 receives a corresponding drive voltage from the data line 1102 to display a corresponding image.
The characteristics of displaying of the known liquid crystal display device 1 will be described as follows.
The liquid crystal display device 1 adopts twisted nematic (TN) mode, which controls the amount of light transmitting through the liquid crystal layer by applying the characteristics that optic chirality of liquid crystal molecules varies with the change of voltage applied. However, when a user views the liquid crystal display device 1 in an inclined direction, contrast of the liquid crystal display device 1 is greatly reduced. Further, when a user changes from viewing the display in an inclined direction toward viewing the display in a front direction, difference of brightness in a number of gray levels from black to white can be obviously perceived. Further, the TN mode liquid crystal display device shows a characteristic of gray level reversal, for example a darker portion when viewed in the front side becoming brighter when viewed in an inclined direction.
Specifically, as shown in FIGS. 3-5, FIG. 3 shows a plot of relationship between a drive voltage applied to the known liquid crystal display device 1 and transmittance, in which curve 301 is a plot of drive voltage and transmittance by taking a front view angle to observe the known liquid crystal display device 1, curve 302 is a plot of drive voltage and transmittance by taking an angle of 30° shifted from the front view angle to observe the known liquid crystal display device 1, and curve 303 is a plot of drive voltage and transmittance by taking an angle of 60° shifted from the front view angle to observe the known liquid crystal display device 1.
FIG. 4 is a plot of standardized transmittance curves by standardizing the curves of FIG. 3 with respect to white displaying, in which curve 401 is a plot of standardized transmittance of observing the known liquid crystal display device 1 at the front view angle, curve 402 is a plot of standardized transmittance of observing the known liquid crystal display device 1 at an angle of 30° shifted from the front view angle, and curve 403 is a plot of standardized transmittance of observing the known liquid crystal display device 1 at an angle of 60° shifted from the front view angle.
FIG. 5 is a plot of gamma (γ) characteristic of the known liquid crystal display device 1. Gamma (γ) characteristic is an indication of the gray level dependence of brightness, wherein gray level displaying condition is changed with the observation direction. Thus, the γ characteristics obtained for observations made at the front view angle and other viewing angles that are shifted from the front view angle (such as that shifted from the front view angle by 30° and that shifted from the front view angle by 60°) are different from each other. As shown in FIG. 5, curve 501 is a plot of gray level characteristic of the known liquid crystal display device 1 taken at the front view angle, curve 502 is a plot of gray level characteristic of the known liquid crystal display device 1 taken at an angle shifted from the front view angle by 30°, and curve 503 is a plot of gray level characteristic of the known liquid crystal display device 1 taken at an angle shifted from the front view angle by 60°. Since great deviations exist between curves 502 and 503 and the front view angle gray level characteristic curve 501, it is apparent that γ characteristic of the liquid crystal display device 1 is poor.
Thus, it is desired to have a liquid crystal display device that overcomes the above problems.